Skip to main content

Full text of "The manufacture and properties of iron and steel"

See other formats

350                         METALLURGY OF IKON" AND STEEL.
jected to the most severe of all tests in the exposure of a hardened edge to the blows of a hammer or the shocks of a planer. The requirements of general practice unconsciously evolved the formula for such metal, requiring low phosphorus, low sulphur and low manganese. In this process of natural selection m mention was made of silicon. Some makers try to keep it as low as possible, but a large part of the best steel has regularly contained, year after year, from .20 to .80 per cent, of this element.
Notwithstanding all this testimony, it is. firmly believed by many practical metallurgists that the presence of even .03 per cent, ma-•terially injures the quality of soft steel. I cannot positively assert the contraxy, but I believe that the effects ascribed to silicon may be due to the conditions of manufacture which gave rise to it. These conditions might be fatal under one practice, as, for instance, when ingots are rolled directly into plates, while they might be harmless, or even beneficent, when an ingot is roughed down and reheated. The opinions of practical men are sometimes of more value than the learned conclusions of theorists,, and must never be ignored, but they are not always inerrant.
SEC. XVIIc.—Influence of manganese.—Spiegel-iron or ferro-'manganese is added to a heat of steel at the time of tapping in order that it may seize the oxygen, which is dissolved in the bath, and transfer it to the slag as oxide of manganese; but this reaction is not perfect, and there is reason to believe that common steels contain a certain percentage of oxygen. Steel low in phosphorus and sulphur requires less manganese than impure metal, although it is difficult to see.why there should be less oxygen to counteract, and this indicates that the manganese prevents the coarse crystallization which the impurities would otherwise induce.
Besides conferring the quality of hot ductility, manganese also raises the critical temperature to which it is safe to heat the steel, for just as it resists the separation of the crystals in cooling from a liquid, so it opposes their formation when a high thermal altitude augments the molecular mobility. These two qualities render manganese one of the. most valuable factors in the making of steel, although it has been used too freely in some cases. Years ago it was regarded as a panacea for all bad practices in the Bessemer and the rolling mill, and steel often contained from 1.25 to 2 per, cent, of manganese, but it was soon discovered that such rails were brittle